1. Field of the Invention
The invention relates to a stud sensing device for detecting objects behind wall linings.
2. Description of Prior Art
Stud detectors are well known and rely on detecting changes in dielectric constant. A portable stud locating device is fully described in U.S. Pat. No. 4,464,622. But the device ignores the effect of wall lining thickness on the accuracy of locating stud edges, and provides no compensation for it.
U.S. Pat. No. 5,352,974 discloses a stud sensor of dual sensitivity. However, experiments show that dual sensitivity is not adequate to accommodate operation of a stud sensor upon walls, which are practically available, of varied thickness ranging from ½ to 2 inches.
U.S. Pat. No. 6,215,293 discloses a stud sensing device comprising a routine of searching for studs for 5 seconds after self-calibration of the device. If no (wood) studs are detected during the 5-second period, the wood stud detection circuit is disabled. This functions as a means to determine the presence of studs behind walls. However, it does not provide a compensating means to eliminate the effect of wall thickness on the accuracy of locating studs.
As different wall thickness affects the accuracy of locating stud edges, a stud sensor with fixed or pre-assigned sensitivity may not be able to locate stud edges accurately enough.